Certain biosensing systems use magnetoresistive (MR) sensors to detect biologically functionalized nanometer-sized magnetic labels. For instance, a biomolecule under test is immobilized on magnetic labels and passed over an array of probe molecules. An MR sensor is used to detect the presence of the magnetic labels. Magnetic labels not bound to the probe molecules are then washed away, and the MR sensor is once again used, this time to detect the presence of magnetic labels that are bound to the probe molecules. Resistance of the MR sensor is proportional to the net magnetic moment of the magnetic labels. A significant change in resistance after washing away the unbound magnetic labels indicates that the magnetic labels did not bind to the probe molecules.
Although these biosensing systems test for the presence of certain biomolecules, they do not test the mechanical properties of biomolecules. Yet in biological testing, there is value in being able to move and manipulate magnetic labels. Valuable information can be learned by testing the mechanical properties of a magnetic label that has bonded to a probe, whether that of a protein detected with an antibody or a DNA fragment hybridizing with another DNA fragment.